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III/115 IUE Atlas of O-Type Stellar Spectra (Walborn+ 1985)
International Ultraviolet Explorer Atlas of O-type Spectra from 1200 to 1900 A
Walborn N.R., Nichols-Bohlin J., Panek R.J.
<NASA Reference Publication #1155 (1985)>
=1985NASAR1155....0WADC_Keywords: Stars, O ; Spectroscopy ; Spectra, ultraviolet ; Atlases
Mission_Name: IUE
Abstract:
The International Ultraviolet Explorer Atlas of O-Type Spectra From 1200
to 1900 A (Walborn et el. 1985) lists normalized fluxes and flux quality
factors, splice points, and identifying information (star name/number,
spectral type, SWP number, and name of the principal investigator) on
101 spectrograms of 98 O-type stars. The primary purpose of this work is
to investigate the existence of systematic trends in the ultraviolet
line spectra of the O stars, including the prominent stellar wind
features, and the degree to which they correlate with the optical
spectral classifications. A subsidiary objective is to identify
ultraviolet features which may themselves prove useful as
classifications criteria.
File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file
stars.dat 100 100 Star IDs, Spectral Types, IUE image
numbers, PI names, atlas page numbers
spectra.dat 80 80800 Fluxes and data quality flags
splices.dat 74 1313 Splice points of spectra
See also:
III/188 : IUE Atlas of B-Type Stellar Spectra (Walborn+ 1995)
III/83 : IUE low-dispersion spectra of normal stars (Heck+, 1984)
VI/99 : Merged Log of IUE Observations (NASA-ESA, 1999)
Byte-by-byte Description of file: stars.dat
Bytes Format Units Label Explanations
1- 10 A10 --- ID HD/HDE or Sanduleak (Sk) number of star
13- 26 A14 --- Name Name of star
29- 44 A16 --- Sp Optical spectral classification
47- 51 I5 --- SWP_num SWP camera image number of observation
52 A1 --- Aper [LS] IUE Large or Small Aperture
54- 69 A16 --- PI_name Name of the IUE principal investigator
72- 73 I2 --- Plate_1 *First atlas plate showing spectrogram
75- 76 I2 --- Plate_2 ?Second atlas plate showing spectrogram
78- 79 I2 --- Plate_3 ?Third atlas plate showing spectrogram
81- 82 I2 h RAh Right Ascension J2000 (hours)
84- 85 I2 min RAm Right Ascension J2000 (minutes)
87- 90 F4.1 s RAs Right Ascension J2000 (seconds)
92 A1 --- DE- Declination J2000 (sign)
93- 94 I2 deg DEd Declination J2000 (degrees)
96- 97 I2 arcmin DEm Declination J2000 (minutes)
99-100 I2 arcsec DEs Declination J2000 (seconds)
Note on Plate_1:
Location of of the spectrogram in the printed atlas. Each plate covers two
pages in the atlas (first page covers 1200-1500 A, and the second page
covers 1500-1900 A). Some spectrograms appear on more than one plate.
Byte-by-byte Description of file: spectra.dat
Bytes Format Units Label Explanations
1- 10 A10 --- ID *HD/HDE or Sanduleak (Sk) number of star
13- 16 I4 0.1nm lambda *Wavelength of first flux/quality pair
18- 26 F9.5 --- flux_1 *Normalized flux at wavelength=lambda
29- 32 F4.2 --- qual_1 *Data quality flag associated with flux_1
34- 42 F9.5 --- flux_2 Normalized flux at wavelength=lambda+0.025 nm
45- 48 F4.2 --- qual_2 Data quality flag associated with flux_2
50- 58 F9.5 --- flux_3 Normalized flux at wavelength=lambda+0.050 nm
61- 64 F4.2 --- qual_3 Data quality flag associated with flux_3
66- 74 F9.5 --- flux_4 Normalized flux at wavelength lambda+0.075 nm
77- 80 F4.2 --- qual_4 Data quality flag associated with flux_4
Note on ID:
There are 800 records for each star, and the ID appears at the beginning of
each record for a given star.
Note on lambda:
The quoted wavelength value is the wavelength of the flux_1 and qual_1 data
pair. The wavelengths for the subsequent flux/qual data pairs in the
record are in increments of 0.025 nm.
Note on flux_1:
See Appendix A: "Data Preparation" for a brief description of how the
normalized flux was calculated.
Note on qual_1:
See Appendix A: "Data Preparation" for a brief description of how this
normalized quality factor was calculated.
Byte-by-byte Description of file: splices.dat
Bytes Format Units Label Explanations
1- 10 A10 --- ID *HD/HDE or Sanduleak (Sk) number of star
11- 18 F8.1 0.1nm splice1 *First splice point
19- 26 F8.1 0.1nm splice2 ?Second splice point
27- 34 F8.1 0.1nm splice3 ?Third splice point
35- 42 F8.1 0.1nm splice4 ?Fourth splice point
43- 50 F8.1 0.1nm splice5 ?Fifth splice point
51- 58 F8.1 0.1nm splice6 ?Sixth splice point
59- 66 F8.1 0.1nm splice7 ?Seventh splice point
67- 74 F8.1 0.1nm splice8 ?Eighth splice point
Note on ID:
There are 13 records for each star, and the ID appears at the beginning of
each record for a given star.
Note on splice1:
Splice points are the wavelength values where overlap of successive orders
of the IUE spectrum have been spliced together. These values come in four
pairs per record, where for each pair:
The first wavelength the beginning of the next (higher) order, and
The second wavelength of the end of the previous (lower) order.
Appendix A: Data Preparation:
This section briefly describes the steps involved in selecting and
processing the data comprising this atlas. The following description was
extracted from an edited version of Walborn et al. (1995).
A.1 Selection
Approximately 200 O stars have short-wavelength, high-resolution data in
the IUE archive. 120 of these were examined for possible inclusion in
the atlas. The primary selection criterion was the availability of
homogeneous optical spectral classifications by Walborn (1972 AJ 77,
312; 1973 AJ 78, 1067). In general, known interacting binaries and very
rapid rotators were avoided, but a number of peculiar objects and
categories which have been well described optically were specifically
included.
A.2 Processing
The IUE Spectral Image Processing System (IUESIPS) data were retrieved
from the IUE data archive. Each gross spectrum included samples of the
observed signal along each echelle order, integrated along a
pseudo-slit; and a corresponding sample of the interorder background.
Sample wavelength and a data quality indicator were also included.
Processing then proceeded through the following steps:
1. The background was smoothed and subtracted from the on-order
signal to yield the net spectrum.
2. A "ripple" correction was applied to adjust for systematic
variation along each order caused by the varying sensitivity of the
echelle grating. Overlap among adjacent orders [was] discarded beyond
the wavelengths at which which the sensitivities [were] equal. These
points of overlap are listed in the second file.
The spectrum was then resampled to 0.25 A resolution:
Each original sample was considered an estimate of the flux averaged
over a bin whose width was equal to the spacing between the adjacent
points. Each new sample was computed as a weighted average of the
original samples; the weight of each original sample is equal to the
fraction of its bin which falls within the 0.25 A window centered on
the new wavelength point. However, the weight is zero for any
original point for which the IUESIPS quality factor indicated
contamination by a camera reseau, saturation of the vidicon camera,
or a particle radiation hit. The new sample points were spaced evenly
at 0.25 A intervals from 1150 A to 1950 A. For each new sample point,
a quality factor was computed as the sum of the weights for the
original samples contributing to the new point. This quality factor
ranges from about 6 at 1200 A (where there is no effect of a reseau,
etc.) to about 4 at 1800 A for IUESIPS processing at GSFC before
November 1981. With the newer version of IUESIPS, this factor is
roughly doubled due to the finer wavelength sampling of the spectrum.
3. The resampled spectrum was then rescaled in order to locate the stellar
continuum at an approximately uniform level:
This ... was performed interactively ... by identifying about a dozen
"continuum" points spaced along the interval 1150-1950 A. Then, the
flux was divided by a cubic spline interpolated through these points.
The intention here was not to precisely define a stellar continuum;
it was simply to place the spectrum onto a convenient scale for
plotting over the full spectral range. The renormalization function
usually showed a broad hump between 1400 and 1600 A. It is unclear
whether this represents a rise in the instrument sensitivity near
1500 A or an effect of blended spectral absorption features near 1400
and 1600 A. Similarly, the data quality factor was normalized to
remove the effect of the decreasing spectral dispersion toward longer
wavelengths, which causes the number of original samples within a
0.25 A window to decrease.
Narrow positive spikes in the flux data due to particle radiation
hits and the geocoronal Lyman alpha emission were eliminated
manually.
In addition, the catalog authors note the following:
Small deviations from unity in the data quality factor occur where a
few of the original sample points in the 0.25 A resample window were
contaminated by a reseau. Large deviations from unity occur where
most or all of the points were affected by a reseau. In many cases,
no effect of the reseau is apparent in the stellar spectrum; this
occurs when the reseau falls close to but not precisely onto the
stellar spectrum, and the interorder background is weak.
Additional Note (December 2000):
The Aperture column ("L" or "S" in column "Aper" of the "stars.dat" file)
has been added at CDS, as well as the star positions.
(End) Joel W. Parker [GSFC/Code 680] 07-Aug-1995